I came across a pdf that staes a 30% improvement in a ASHP COP can be realized by pre conditioning the air.
PDF is on a big system requiring 3600 CFM in fan power pushing air through three 8 inch pipes buried 5 feet deep
EFFECT OF OUTDOOR AIR PRE-CONDITIONING ON ASHP PERFORMANCE USING EAHE
https://www.ryerson.ca/content/dam/g...0S.%20Fung.pdf